In the related art, a stretch yarn using stretch fibers such as those of rubber has been used in underwear, socks or sportswear. The stretch yarn such as a single-covered yarn has also been used in knitted products such as sweaters (refer to Japanese Unexamined Patent Publication JP-A 09-324334 (1997), for example). This single-covered stretch yarn is formed by singly winding a core yarn of highly stretchable polyurethane around a sheath yarn of other fibers. A double-covered stretch yarn which a sheath yarn us doubly wound is also fabricated (refer to Japanese Unexamined Patent Publication JP-A 10-077538 (1998), for example). Polyether-ester is also used in the core yarn to be covered (refer to Japanese Unexamined Patent Publication JP-A 08-325874 (1996), for example). The core spun yarn, which is spun to have the core yarn of the stretch fibers surrounded by other fibers, is also used as the stretch yarn (refer to JP-A 2003-073947, for example).
Knitted products are characterized by having a specific feeling on the basis of knitting loops. There has already been developed a method for producing a knitted product having a desired feeling with an ordinary knitting yarn other than a stretch yarn while controlling a loop length of the stitches (refer to Japanese Examined Patent Publication JP-B2 2676182, for example). In this knitting, the control of the stitch loop length is important so that a feeding device for the necessary stitch loop length has also been developed (refer to Japanese Unexamined Patent Publications JP-A 11-500500 (1999) and JP-A 2002-227064, for example).
The methods of JP-B2 2676182 and JP-A 2002-227064 are supposed to use the ordinary knitting yarn other than the stretch yarn. The introduction of “Detailed Description of the Invention” of JP-A 11-500500 describes that the invention relates to an electronic control feeding device containing the stretch yarn. This feeding device is provided with a stretch sensor so that the device feeds the knitting yarn to knit the stretch yarn under a predetermined tension. However, this device is deficient in the knitting of a variable texture such as knit, tuck and miss stitches. Although the tension can be set on the stretch yarn used, what feeling a fabric knitted under the set tension takes is not known before the fabric is actually knitted. For the desired fabric, therefore, the try-and-check has to be continued to take a long time period for the production.